1. Field of the Invention
The present invention relates to a device and a method for charging batteries with a sinusoidal wave, particularly to a device and a method that automatically traces and fixes a resonance frequency of the batteries for offering an optimal charging frequency to the batteries.
2. Description of the Related Art
The great progress and speedy development of the electronic techniques have popularized the portable electronic devices such as cellphones, laptops, and MP3s, which adopt a secondary battery to serve the main power source. While the recyclable energy and the motor-driven vehicles are greatly developed, energy storage systems for batteries become essential subsystems. Obviously, techniques for charging batteries grow to be important. Common techniques for charging batteries such as the Constant Trickle Current Charge (CTC), the Constant Current (CC), and the Constant Current and Constant Voltage (CC-CV) are generally utilized (REFERENCE 1). Wherein, the CC-CV is the most popular means for charging batteries. However, the CC-CV provides unsatisfactory charging efficacy. Thereby, charging means such as the artificial neural network, the genetic algorithm, the ant algorithm, and the grey prediction are applied for enhancing the charging efficacy (REFERENCES 2-6). However, afore charging means actually consist of complicated circuits and the costs thereof are also high. Accordingly, another charging means that applies the phase-locked loop technique is adopted for speedily charging batteries with a low circuit cost (REFERENCES 7 to 10). The pulse wave charging means is also commonly applied for charging batteries today. Such charging means allows ions in electrolyte of the batteries to be spread evenly and postpones the polarization of the batteries so as to accelerate the charging speed and enhance the using life (REFERENCE 11). In fact, a charging frequency in the pulse wave charging system determines the charging speed and the charging state. A conventional way to find out the optimal charging frequency utilizes the empirical approach or the trial and error method. However, these means do not discuss how to determine the optimal charging frequency (REFERENCES 12 to 16). In order to modify the conventional charging means with an objective manner, the alternate current property of batteries must be acquainted. FIG. 1-A shows an AC Impedance Model that comprises a Charge Transfer Resistance Rct, a Warburg Impedance zw, an electrode parallelly connected to a Capacitance Cd in an electrolyte, an Ohmic Resistance Ro serially connected to an Electrode Inductance Ld, and an Ideal Battery (REFERENCES 17 to 19). Wherein, the battery is turned to an equivalent model, and circuits thereof adopt one impedance Zbattery that is serially connected to one Ideal Battery. FIG. 1-B shows that the battery equivalent model is analyzed through a circuit means. Namely, two ends of the battery are respectively added with a variable frequency. While the frequency is changed, the impedance of the battery is varied accordingly. Whereby, a loss state of the battery capacity could be controlled by the frequency of the power. That is to say, if an optimum energy transferring efficiency is to be served to the battery in time of charging, a minimum impedance of the battery has to be adopted. That is because under such frequency, the battery temperature does not raise largely, and the using life of the battery could be concurrently prolonged.
Accordingly, the present invention utilizes a resonance frequency fr that charges batteries with a sinusoidal wave, automatic tracing function, and a fixed current. While the resonance frequency fr is adopted in a charging device and served as the optimum charging frequency, the using life of the batteries could be extended.